The invention relates generally to marine propulsion devices, to propeller shafts included in marine propulsion devices, and to propellers mounted on such marine propulsion device propeller shafts. The invention also relates generally to dampers.
The relatively large weight of a propeller positioned at the end of a cantilevered propeller shaft causes bending vibrations during propeller shaft rotation. Such bending vibrations have caused failure by reason of cracking of the gearcase, breaking of the bolts connecting the drive shaft housing and the powerhead, and breakage of the propeller shaft itself.
More particularly, propeller vibration can cause substantial lateral vibration when large horsepower engines operate at wide open throttle. Such vibration causes lateral forces on a propeller shaft, which forces substantially exceed the thrust developed by the propeller and transmitted to the propeller shaft.
In the past, torsional dampers have been placed on drive shafts. Such dampers were characterized by dynamic elements which were attached to a flywheel by a thin elastomeric layer along the outside of the flywheel.
Attention is directed to the following U.S. Pat. Nos.:
______________________________________ 3,126,760 T. H. Peirce March 31, 1964 3,242,1791 J. D. Smith March 29, 1966 3,334,886 A. Caunt August 8, 1967 3,362,251 J. J. Francis January 9, 1968 3,603,172 J. Hall September 7, 1971 3,990,324 Fishbaugh, et al. November 9, 1976 4,207,957 Sivers, et al. June 17, 1980 4,220,056 R. C. Bremer, Jr. September 2, 1980 4,395,809 J. L. Whiteley August 2, 1983 4,642,057 Frazzell, et al. February 10, 1987 4,701,151 Vehera October 20, 1987 ______________________________________